Hello.

I am trying to develop a suitable current transformer to measure currents from 0 to 2A rms. Things are not going very well.

To start with, let me explain I tried with different ratios and no matter what I do, I end up with the same somewhat distorted shape (tough different amplitudes).

Test setup is: a 50Hz/45VA transformer with 10 Vrms output (note clipped sinewave), which is connected to a power resistor. The current flows through the power resistor into the primary of the CT (ratio is

2:60), the CT secondary is terminated by a 0.33 ohm resistor and the voltage across it is amplified by a factor of 100 with a differential opamp.Pictures can be viewed here:

Questions:

Why the ratio error?

When I measured the frequency response of the CT I got surprising results. First: measuring the secondary inductance on a RCL meter resulted in inductance X. But when measuring the inductance from a few Hz to about 100kHz shows an inductance of X/2. Why?

Another problem is the resistance of the secondary, which is on average say half of the secondary reactance @50Hz.

Now suppose I want to have two indipendent secondaries on my CT, both terminated with a 0.33 ohm burden. How would this effect my "new" CT?